内蒙古乌拉特后旗乌兰敖包地区二叠纪中-基性火山岩地球化学、年代学、Hf同位素特征及其地质意义  

GEOCHEMISTRY,CHRONOLOGY AND HF ISOTOPE FEATURES OF THE PERMAIN INTERMEDIATE-BASIC VOLCANIC ROCKS IN WULANAOBAO AREA,URAD HOUQI,INNER MONGOLIA AND ITS GEOLOGICAL SIGNIFICANCE

作　　者：郭硕 滕学建 刘洋[1] 滕飞 何鹏[1] 王文龙 田健 段霄龙 

机构地区：[1]中国地质调查局天津地质调查中心,天津300170

出　　处：《地质力学学报》2017年第3期397-410,共14页Journal of Geomechanics

基　　金：中国地质调查局地质调查项目(12120113056300;121201006000160902)

摘　　要：内蒙古乌拉特后旗乌兰敖包地区中-基性火山岩位于华北陆块北缘西段,野外出露岩性主要为灰黑色-深灰绿色玄武岩、深灰绿色玄武安山岩和灰绿色安山岩等。岩石样品中SiO_2含量49.33~65.84%,Na_2O含量0.53~5.49%,K_2O平均值为0.25~6.40%,属于钙碱性系列;由基性到中性岩石中稀土总量呈增加趋势,轻稀土元素富集程度增加,δEu负异常逐渐明显;微量元素显示火山岩普遍具有不同程度的Ta、Nb亏损,U、Ba、K等大离子亲石元素富集特征,具有俯冲带弧岩浆岩的特征。火山岩中岩浆锆石U-Pb测年结果为285.0±2.3 Ma和265.0±1.5Ma,表明其形成时代为早-中二叠世;火山岩与下伏地层接触关系及捕获锆石的年龄特征指示,乌兰敖包地区火山岩形成在华北陆块北缘之上。锆石Hf同位素信息指示岩浆起源于受俯冲板块影响的亏损地幔,岩浆上升过程中加入了壳源物质。The Wulanaobao intermediate-basic volcanic rocks, distributed in Urad H o u q i, Inner Mongo l i a, are located in the western north margin of the north China block. T h e outcropped lithologies mainly are grey black- spruce basalt, spruce basaltic andesite and greyish-green andesite. All samples show chemical signatures of calc- alkaline series which are characterized by contents of Si0 2 （49. 33 -65. 84% ）,N a 20 （0？ 53 ？5. 49% ） and K 20 （0. 25 -6. 40% ） From basic to intermediate, the a m o u n t of rare earth elements, light rare earth elements enrichment degree and Eu negative anomaly degree show a trend of increase. T h e trace elements show subduction zone arc magmatite features which are characterized by wide depletion of T a and N b , and enrichment of the large ion lithophile elements （ U , Ba , K ） . T h e zircon U - P b dating results of the m a g m a from volcanic rocks are 285. 0 土 2. 3Ma and 265. 0 ± 1. 5Ma,which indicates that the volcanic rocks were formed at the early-middle Permian period. The age characteristics of captured zircons and the contact relations between volcanic rocks and underlying strata suggest that volcanic rocks from W u l a n a o b a o were formed on the crust of the north China block. Zircon H f isotopic information indicates that the magma w a s derived from the depleted mantle which was affected by the subducting plate and partly joined with crust-derived material during the rising stage.

关 键 词：兴蒙造山带 中-基性火山岩 二叠纪 地球化学 大陆边缘弧 

分 类 号：P581[天文地球—岩石学]